Solid ink (also known as phase-change ink) printers conventionally employ ink supplied in solid form, either as pellets or as colored ink sticks. In general, phase change inks are in solid form at ambient temperature, but the ink must be converted to liquid form and transported to the print head, where the ink can be ejected as drops or jets. Generally, this phase change is accomplished by melting the solid ink. At the inkjet head, droplets of molten ink are ejected from a print head, forming jets of ink that print on the target media. When the ink droplets contact the printing media, they quickly solidify to create an image in the desired pattern.
In conventional inkjet imaging devices, feed channels connect the inkjet heads to the image-forming apparatus that may include an ink melting apparatus, transporting the ink from the ink melting apparatus to the inkjet heads. As the solid ink must be melted before transportation, some systems couple a heater assembly with each feed channel to melt and maintain the liquefied solid ink at a predetermined temperature during transportation.
For efficient printer operation, the heater assembly should heat the ink uniformly and quickly, as uneven heating of the ink may result in “hot spots” or “cold spots,” which may produce non-uniform images. For example, if the ink is overheated, the color dyes or pigments may be damaged, resulting in image color shifts. If a cold spot exists, the ink may not flow well, possibly leading to shifts in image color due to ink viscosity variation. Further, the image-forming apparatus should monitor the temperature of the feed channel as overheating may melt the feed channels, and under-heating may create cold spots.
Typical ink-heating systems utilize an external heater assembly coupled to feed channel. The heating provided by the external heater depends on the thermal contact with the feed channels; the external heater may not provide consistent ink heating, resulting in cold and hot spots. Moreover, the inaccuracy in thermal coupling between the heater and the feed channel can result in overheating of the heater, and heater failure.
Thus, there remains a need for a device that quickly and uniformly heats/melts or maintains liquefied solid ink at a predetermined temperature during transportation from the image-forming device to the print heads, provides temperature-sensing capabilities, and is cost effective.